Frequently, there is a need to draw fluid from a larger body of fluid where the quality and content of the fluid are relatively uncontrolled. A common example is drawing water from a pond, river, canal, or ditch for irrigation of agricultural lands. The water in such bodies frequently is full of debris which can be floating on the water's surface, suspended in the water, and resting on the bottom of the body. The debris can range in size and shape from trees or large tree limbs to small leaves and pieces of paper.
This debris presents several problems when the water is drawn by pump suction pipes. First, the debris can clog the inlet from the pump to the water source and prevent any water from being drawn. Also, smaller pieces of debris capable of passing through the pump inlet can cause damage to the pump which results in time loss and repairs costs from frequent breakdowns.
Separating liquid effluent from solid waste in waste treatment plants presents the same types of problems. The solid waste will either clog up the suction intake of the pump or pass into the pump causing pump failure. These types of problems occur whenever fluid is drawn from a body containing non-fluid debris.
This problem and attempts to solve it are well known. The obvious solution is to cover the end of the pump suction pipe inlet with a simple filter that allows passage of the water while blocking debris above a certain size. These simple filters suffer from the same sort of clogging problems discussed above and therefore have a limited usefulness.
Other attempts to solve these problems have used a more sophisticated filter that uses a rotary cylindrical filter screen assembly. Typically, the rotary cylindrical filter screen assembly rotates about stationary nozzles that direct spray against the inside of the filter screen assembly in an attempt to force debris away from the outside of the filter screen assembly.
While these filters are an improvement over the simple filter in some ways, they also present problems. First, a motive force must be provided to cause the rotary cylindrical filter screen assembly to rotate. In the larger versions of this type of filter, considerable force may be required to rotate the filter screen assembly.
The cleaning feature of this filter type will not function if the filter screen is prevented from rotating. As a result, the entire rotary cylindrical filter screen assembly must be held out of contact with other objects to ensure that it functions correctly. If the filter screen assembly is allowed to rest against the side or bottom of the body of the fluid, it will stop turning and the filter will clog quickly. The same thing can happen if a large piece of debris becomes entangled with the filter screen assembly. This filter, thus, does not provide a reliable solution to the problems.
As illustrated by the above discussion, there are a number of desirable features for a self-cleaning filter. It would be desirable to have a filter that was continually self-cleaning. It also would be desirable to have a self-cleaning filter that is reliable. Further, it would be desirable to have a self-cleaning filter that can operate regardless of the environment into which it is placed or the way it is oriented. In addition, it would be desirable to have a self-cleaning filter that is inexpensive and easy to maintain.
While the discussion herein relates to a self-cleaning filter, it is not intended that the invention be limited to this situation. It will be obvious from the description that follows that the present invention will be useful in other applications with problems common to those described herein.